Introduction to P&ID

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The flow sheet or flow diagram are often used in context of engineering and design application. Although this terminology is not most accurate to describe P&IDs, it’s sufficient to describe the overall family of a process based diagram to which P&IDs belong.

We can divide the process diagram in three type or step:

BFD : The Block Flow Diagram
PFD : The Process Flow Diagram
P&ID : The Process and Instrumentation Diagram

BLOCK FLOW DIAGRAM

The beauty of a BFD is its ability to outline the complete process on little more than a single sheet. The diagram usually resemble an organized chart, containing mainly text enclosed by boxes, interconnecting lines, the process commodities they transport and flow arrows to indicate flow directions.

INFORMATION PROVIDED BY A BFD

A good BFD typically contains the following:

• Individual pieces of equipment or equipment package that are denoted by a single symbol, typically a rectangle.
• Clear label illustrating function
• Lines linking equipment or process to show flow direction.
• The order of process flow arranged and if possible with a gravity bias.
• Whenever more than one line leaves a process then the processed commodity in each line should be clearly marked

TYPICAL BFD

PROCESS FLOW DIAGRAM

Process flow diagram carry more information than the block flow diagram. They show more detail about major equipment & sub system and the flow. PFD include information of the pressure and temperature of the feed and product line to and from all major equipment. Also indicate the main header and points of all control. It’s consider as the precursor of P&IDs

Information provided by a PFD

A typical PFD shows the following items:

• Process piping
• Process flow direction
• Major bypass and recirculation lines.
• Major equipment represented by simplified symbols.
• Control and process critical valves
• System ratings and operational values.
• Composition of fluids
• Connection between systems.

TYPICAL PFD

PROCESS AND INSTRUMENTATION DIAGRAM

The Piping and Instrumentation Diagram (P&ID), based on the Process Flow Diagram (PFD), represents the technical realization of a process by means of graphical symbols for equipment and piping together with graphical symbols for process measurement and control functions.

A P&ID carries a wealth of information that span engineering disciplines to define a process. The representation and designation of all the equipment, instrumentation and piping should comply with the requirements of Standard. Auxiliary systems may be represented by rectangular boxes with reference to the separate diagrams

For processing facilities, it is a pictorial representation of:

Ø Key piping and instrument details

Ø Control and shutdown schemes

Ø Safety and regulatory requirements and

Ø Basic start up and operational information

INFORMATION PROVIDED BY P&ID:

• Permanent start-up and flush lines.
• Flow directions and Interconnections references.
• Control inputs and outputs, interlocks and Computer control system input.
• Interfaces for class changes.
• Identification of components and subsystems delivered by others.
• Instrumentation and designations.
• Mechanical equipment with names and numbers.
• All valves and their identifications.
• Process piping, sizes and identification
• Miscellaneous - vents, drains, special fittings, sampling lines,reducers, increasers and swagers.

TYPICAL P&ID

More about PFD
More about P&ID 

PIPING DAIGRAM SYMBOL

Symbol is the basic notation to describe or represent a P&ID. To read and interpret piping and instrument drawing , the reader must learn the meaning of the symbol. We will discuss about the common symbols that are used to depict fluid process plant.

In general all the symbols used in P&ID are as per ISA or ANSI standard. But any organization may have their own standard which is derived from international standard.

LINE SYMBOL

COMPRESSOR SYMBOL

FUNCTION SYMBOLS

FUNCTION SYMBOLS

PUMP SYMBOLS

STORAGE SYMBOL

FITTINGS SYMBOL

EXCHANGER SYMBOL

Piping Symbols used in P&ID

Symbols for several types of valve generally used in process plant:

____________________________________________________________________

Notation used to describe a valve's position(Open/Closed/Partially open etc):

____________________________________________________________________

Symbol and abbreviation used for identifying types of instruments and their function:

____________________________________________________________________

Miscellaneous symbol used to mention direction and continuity:

P&ID ABBREVIATION AND IDENTIFICATION

Abbreviation is used to define:

1. An equipment to specify its type or service.
• Example: For a Pump generally ’AP’ abbreviation is used for numbering. AP1002, AP6009 etc.
• Example: For a Vacuum Pump generally ’AV’ abbreviation is used for numbering. AV1012, AP4007 etc.
• Example: For a storage tank 'ST' and for vessel 'AB' is used for numbering.
2. A pipe line to specify its service.
   
• Example: ‘CWR’ is used for the Cooling Water Supply line.
• Example: ‘HOS’ used for Hot Oil Supply line.
3. An Instrument to define its function.
   
• Example: ‘PRV’ used for control valve to Control Pressure.
• Example: ‘FIC’ used for Instrument which is used to Indicate and Control Flow.

Bellow is list of some abbreviation generally used in a standard P&ID:

DRAIN/SEWER ABBREVIATION



MISCELLANEOUS ABBREVIATION



ABBREVIATION FOR UTILITY SERVICE



ABBREVIATION FOR UTILITY SERVICE




INSTRUMENT ABBREVIATION

Know P&ID

More about P&ID

A P&ID sheet can be divided in following parts:

• Title Block (1st block, 2nd block, 3rd block & other information as scale, soft copy reference etc.)
  
  
• Grid System
  
  
• Revision Block
  
  
• Notes and Legend
  
  
• Equipment Specification
  
  
• Drawing (Graphic Portion)
  
  

TITLE BLOCK:

Generally title block consist 3 Area: 1st area contains drawing title, number, location or area, site and vendor. 2nd area contains signature, information of drafting, verification, approval and control. 3rd area is reference area which contains reference block and drawing information.

DIFFERENT AREA OF A TITLE BLOCK SHOWN BELLOW:



BELLOW IS AN EXAMPLE OF A TYPICAL TITLE BLOCK:



GRID SYSTEM:


Because of drawing tend to be large & complex it quite difficult to find a specific point in a sheet. This is especially true when a wire or pipe is continued on a second drawing. To locate the point in reference print most drawing has 2D coordinate grid system. The grid consist letter, number or both that run horizontally and vertically around the drawing.

TYPICAL GRID USED IN P&ID:



REVISION BLOCK:

If any change is done in a system or equipment or specification in drawings the drawing must be redrafted and reissued with a new version of the original drawing.The revision details must be mentioned in Revision Block. The original drawing must be of version 0.



NOTES AND LEGEND:

Because of the importance of understanding all the symbol & convention used in a drawing the notes and legend section must be review before reading a drawing.The legend and note section of a drawing list & explain any special symbol & convention used on the drawing. Any notes required for understanding a drawing can be mentioned here.




EQUIPMENT SPECIFICATION:

In this section the specification of essential equipment can be mentioned.

• A vessel/ tank can be specified with capacity, MOC, Empty weight, jacketing detail, tubing detail etc.
  
  
• A pump can specified with it’s disch. capacity, head, RPM, drive type etc.
  
  
• A motor can be specified with it’s RPM, rating current, voltage, frequency etc.
  
  

DRAWING:

Drawing area is the graphics section where the pictorial view of system/project/equipment is described graphically using standard symbol & procedure.

EXAMPLE OF A STANDARD DRAWING SHEET:




Generally any organization customizes and makes their own standard focusing on ISA standard.